import java.util.Random;

public class InvariantBreaking {
	final static int MIN=0, MAX=100;
	
	private volatile int lower=MIN, upper=MAX; // upper must be bigger than lower
	int nbrInconsistencies=0;
	
	public void setLower(int value) { 
	   if (value > upper) 
		   return; // don't change value
	   lower = value;
	}
	public void setUpper(int value) { 
	   if (value < lower) 
		   return; // don't change value
	   upper = value;
	}
	public boolean checkInvariant(){
		if (upper < lower){
			System.err.println("Invariant is broken! upper < lower ("+upper+" < "+lower+")");
			nbrInconsistencies++;	
		}
		return upper < lower;
	}
	public String toString(){ return "["+lower+", "+upper+"] "+nbrInconsistencies+" inconsistencies"; }
	
	/**
	 * STANDALONE PROGRAM
	 */
	public static void main(String[] args) {
		final InvariantBreaking invariantBreaking = new InvariantBreaking();

		final int NBR_THREADS=4;
		for(int i=0;i<NBR_THREADS;i++){
			final int I = i;
			new Thread(){
				public void run(){
					Random r = new Random();
					for (int i = 0; i < 1000000; ++i) {
						if (I%2 == 0)
							invariantBreaking.setLower(r.nextInt());
						else
							invariantBreaking.setUpper(r.nextInt());
						invariantBreaking.checkInvariant();
					}
					
				}
			}.start();
		}
		
	}

}